1. Field of the Invention
The present invention relates to a composition for piezoelectric ceramics suitably for composing ceramic vibrators, ceramic filters, ceramic discriminators, ceramic resonators and the like.
2. Description of the Related Art
As compositions for piezoelectric ceramics suitably for composing ceramic vibrators, ceramic filters, or ceramic discriminators, compositions of PbTiO.sub.3 or PbTiO.sub.3 -PbZrO.sub.3 are conventionally well known, and many improvements have been proposed.
For example, generally known are materials of PbTiO.sub.3 -PbZrO.sub.3, to which MnO.sub.2, Cr.sub.2 o.sub.3 and the like are added, for simply improving coefficient Qm of mechanical quality; materials of PbTiO.sub.3 -PbZrO.sub.3, in which perovskite compound such as Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 or Pb (Mg.sub.1/3 Nb.sub.2/3)O.sub.3 as second or third components are made solute, for heightening porcelain characteristics; and the latter to which MnO.sub.3, CrO.sub.3 and the like are added for enhancing coefficient Qm of mechanical quality. Further, for improving temperature characteristic of electromechanical coupling coefficient or resonance frequency fr, known is that where the portion of Pb among the above mentioned components is substituted with Ba, Sr or Ca (Unexamined Japanese Patent Publication (kokai) Nos.6-333427, 7-30169, 7-82021, 7-187777 and 7-187778).
Recently, markets of portable terminal instruments of electronic information such as cellular phones are rapidly growing. Since these portable instruments undergo severe environmental changes (in particular, temperature change), electronic parts having excellent resistance against thermal shocks by temperature change under using circumstances, are required. However conventional compositions for piezo electric ceramics were concerned with problems that thermal shock resistance was inferior, changes occurred in piezoelectric characteristic or resonance frequency due to changes in temperature circumstances, and composed ceramic vibrators did not normally work.
There were the same problems in not only portable terminal instruments but also those for composing ceramic vibrators or the like for communication equipment to be installed in vehicles of furious changes under using circumstances.
On the other hand, by miniaturizing and laminating electric devices, mounting of electronic parts to substrates at high density is advancing and types of miniaturized electronic parts are changing from existing types having leading wires to those mounting in surface. Since parts for mounting in surfaces are exposed to temperature of around 250.degree. C. in a reflow furnace when mounted, they must have excellent heat resistance. In regard to existing types having leading wires, by making solder non-Pb, welding temperature trends to be set at higher than theretofore, and reliability to soldering temperature is desired to be more improved.
However, there was a problem that although conventionally known composition of piezoelectric ceramics was excellent in heat resistibility, it was inferior in thermal shock resistance by temperature change under using circumstance, and if it composed electronic parts to be served in portable telephones or products violent in changes of temperature circumstances, piezoelectric characteristic was deteriorated by temperature change and it was difficult to compose electronic parts at which the present invention aims.
Generally when the piezoelectric ceramics are used to the ceramic vibrator, the coefficient (Qm) of the mechanical quality is demanded to be high as the characteristics of the piezoelectric ceramics (e.g., 500).